FENDER RUMBLE 75 is weird

When i got my Fender Rumble 75, i was practicing with my band, and it suddenly stopped working, then i sent it back to fender in sydney to fix it up, they did. two weeks later i start playing at a gig, now it crakles on standbye and while i am playing.
i have no idea whats wrong with it, and i cant afford (money wise) going to sydney again. is there any way i can fix it at home?